A 2009 file photo of a man standing in the corridor of a former 'black jail' in Beijing, China. Photo: AP

A Beijing court has sentenced 10 people to up to 18 months in jail for illegally detaining petitioners from another city, state media reported on Sunday, in a rare case of the judiciary taking on the shadowy men who operate on the margins of the law.

Those convicted were hired by authorities from Changge city in central Henan province to stop petitioners airing their grievances in Beijing, the People’s Daily said on its website, citing a Beijing newspaper.

They held them in rented houses in a Beijing suburb where the petitioners said they were beaten, the report said.

The men wore badges identifying them as employees of the Beijing representative office of the Changge government, it added.

Petitioning officials has deep roots in China, where courts are seen as beyond the reach of ordinary people, who often try to take local disputes ranging from land grabs to corruption to higher levels in the country’s capital Beijing.

But studies show only small numbers are ever able to resolve their cases through petitioning.

In many cases, petitioners are rounded up in Beijing by men hired by provincial authorities to prevent the central government from learning of problems in China’s outlying regions.

They are often forced home, or held in “black jails” in Beijing.

Despite international criticism, China has continued to run these so-called black jails - unlawful secret detention facilities used to hold critics and petitioners, where detainees are often subjected to beatings, sleep and food deprivation, as well as psychological abuse.